Python 3 Fix: Absolute Imports

Use absolute imports instead of relative imports for python 3
compatability.

Change-Id: I1203ad26c66ab799955c7cb46ea1a98d7f512a41

zuul/merger/server.py

@@ -19,7 +19,7 @@ import traceback
 
 import gear
 
-import merger
+from zuul.merger import merger
 
 
 class MergeServer(object):

zuul/rpclistener.py

@@ -21,7 +21,7 @@ import traceback
 import gear
 import six
 
-import model
+from zuul import model
 
 
 class RPCListener(object):

zuul/scheduler.py

@@ -28,10 +28,10 @@ import threading
 import time
 import yaml
 
-import layoutvalidator
-import model
-from model import Pipeline, Project, ChangeQueue
-from model import ChangeishFilter, NullChange
+from zuul import layoutvalidator
+from zuul import model
+from zuul.model import Pipeline, Project, ChangeQueue
+from zuul.model import ChangeishFilter, NullChange
 from zuul import change_matcher, exceptions
 from zuul import version as zuul_version